Microwave ovens are commonly used in households for warming, and sometimes for cooking food. However, microwave ovens do not heat foods in the same manner as traditional ovens. Traditional ovens have a heat source which is located exterior of a food item being cooked. Heat is transferred from the heat source of the conventional oven to the surface of the food, and then passed by conduction from the exterior to the interior of the food item. This type of heat transfer mechanism requires that the outer regions of the food be heated to higher temperatures than interior regions, such that a thermal gradient will exist to cause heat transfer from the exterior surface to the interior regions of the food. Since traditional cooking ovens, at least initially, heat the exterior of food items to higher temperatures than the interior, the exterior regions of the food items are cooked first, and are often seared to contain moisture within the interior regions of the food items being cooked. After a sustained period of time within a traditional oven, the temperatures of the interior regions of the food items may approach the exterior temperatures.
When food is cooked in microwave ovens, typically the interior of the food is heated to higher temperatures than the exterior of the food. Microwave energy permeates a food item, such that interior regions of the food item will be cook faster than the exterior perimeter. The exterior perimeter of the food item being cooked is typically exposed to ambient air within the microwave oven, which is typically at ambient or room temperatures. The ambient temperature air within the cooking compartment of the microwave oven will absorb heat from the exterior perimeter of the food, cooling the exterior perimeter to temperatures which are lower than those in the interior regions of the food item. The higher temperatures of the interior regions cause moisture to out-gas from the interior regions and move toward the cooler exterior perimeter of the food, resulting in moisture saturation of the region of the food item adjacent to the exterior perimeter of the food. The typical result is that the exterior surfaces of food items cooked in microwave ovens become spongy or mushy due to the moisture saturation at the exterior peripheral surfaces of the food.
For some food items, such as meats, poultry, fish, breads and the like, it is desirable to heat the exterior regions of the food to higher temperatures than the interior regions so that the exterior regions will become dry while the interior regions remain moist. Although microwave ovens can heat food faster than traditional cooking ovens, microwave ovens have not replaced traditional ovens since it is often preferable to heat food items such that the exterior regions of the food items are dryer than the interior regions of the food items.